| Check | How | Verdict |
|---|---|---|
| 1. Thermostat | Compare upper/lower hose temps warm; boil-test the opening temp | Big hose temp difference, or opens late/never = replace |
| 2. Water pump | Weep-hole dripping, pulley play, impeller erosion | Any of these = replace |
| 3. Radiator | Outside: oil film & debris; inside: scale-clogged tubes | Blow out / remove & flush; badly folded fins = new core |
| 4. Radiator cap & system pressure | Pressure-test the cap | Won't hold rated pressure = new cap first |
Run it hot and the chain reaction starts: head gasket → coolant in oil / white smoke → warped head. The bill grows from a small part to an engine job. Stop, cool down, run the table above — never work a hot machine.
Boundary: continuous overheating + white smoke + milky oil = head gasket or head, treat it as an engine job.
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In an emergency yes, but cold running and higher fuel burn follow; fit a new one soon.
Check for milky oil and coolant loss; if both are normal, resume work.
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